I don't know if it means much (could be a MacOS thing), but WiFi Guard doesn't show some hostnames on MacOS. It does it only for some devices (3 out of 14). I'm an embedded engineer so I rely on my local microcontroller hostname to differentiate it from others.
I've used WiFi Guard on Windows for years now and I was always able to see the hostname. Anyways, it's not a deal breaker since I can set names inside WiFi Guard but meybe it could be improved
If you are interested in technical details, on macOS we use three methods to get device names:
If a device does not reply to any of these, I am afraid its name cannot be determined. Since microcontrollers are lightweight devices, it's likely they don't support reporting their name.
You may still be able to see their names in your router's DHCP lease list, but that's because they would specify their name when requesting an IP address via DHCP. It is stored within the router and WiFi Guard cannot access that information.